The present invention relates to an optical recording medium and an optical read/write apparatus for reading information from and writing information to the optical recording medium.
One kind of optical recording medium is a phase change optical disk. With a phase change type optical disk a groove track is formed on the optical disk to guide the optical beam and for reading and writing information, and a land track between two neighboring groove tracks along a radial direction of the disk is also used for reading and writing information. In short, both the groove track and the land track are used as a recording track, which is called the xe2x80x9cland groove recording methodxe2x80x9d. In the land/groove recording method, a space between two neighboring recording tracks ((the land track)+(the groove track)) along the radial direction is one half of the space between two neighboring groove tracks along the radial direction. By carefully selecting the depth of the groove, crosstalk between the land track and the neighboring groove track decreases.
In the optical disk, the recording track is divided into a plurality of sectors as a data unit of predetermined length. A header including address information such as sector number is previously set at the head part of each sector. This header is formed as a  pattern of a prepit sequence on the surface of the disk.
When using both the land track and the groove track as the recording track, the decrease of crosstalk is only affected for two neighboring recording tracks (the land track and neighboring groove track). Crosstalk greatly increases around the prepit sequence section in the recording track. Therefore, as shown in FIG. 1, the prepit sequence is not located on the recording track but on the middle position between the land track and the neighboring groove track by cutting the groove track at equal spaces. A space between two neighboring prepit sequences is two times the width of the recording track (the width of the land track or the width of the groove track). In FIG. 1 the prepit sequence P0 is commonly used by the land track L0 and the groove track G0, the pit sequence P1 is commonly used by the land track L1 and the groove track G1; the pit sequence P2 is commonly used by the land track L2 and the groove track G2 in order to avoid crosstalk.
In the case of locating the prepit sequence on the middle position between the land track and neighboring groove track by cutting the groove track at equal spaces, the prepit sequence section is not used as the data recording track. Therefore, in the optical disk such as a DVD-RAM of the prior art, each prepit sequence section P0, P1, and P2 is located along the radial direction from inner circle to the outer circle as shown in FIG. 1. As a result, a length of one circle of the optical disk is a product of the sector length and a positive integer. Because of the limitation on location of the prepit sequence, actual linear recording density is set low in comparison with an upper limit of linear recording density along the track direction. Furthermore, a length of one sector on the outer track is longer than a length of one sector on the inner track.
Therefore, the linear recording density of the outer track is lower than the actual linear recording density. As a result, total recording quantity on the entire surface of the disk is lower than a quantity determined by the upper limit of the linear recording density.
In order to avoid a loss of the recording quantity caused by the limitation of the prepit sequence location, for example, a ZCLV (zone constant linear velocity) method is applied. In this method, as shown in FIG. 2, the surface of the disk is divided into a plurality of zones (rings). In each zone, a plurality of the prepit sequence sections are arranged. The area of each sector in one zone is then equal, and the number of sectors increases in proportion to outer circle of the zone. However, in this method, the loss of recording quantity remains because of the limitation of the sector length. Furthermore, other factors causing the loss of the recording quantity (for example, non-use of the recording track neighboring the prepit sequence section over a boundary of the zone) occur.
As mentioned-above, in the optical recording medium of the prior art, by limiting the location of the prepit sequence, the recording quantity is smaller than the recording quantity of the surface of the disk determined by the upper limit of the linear recording density.
It is an object of the present invention to provide an optical recording medium and an optical read/write apparatus to greatly increase the recording quantity without limiting the location of the prepit sequence.
According to the present invention, there is provided an optical recording medium on which a land track and a groove track are formed as a recording track to read and write information, comprising: a prepit sequence formed on the middle position between the land track and the groove track neighbored by unit of predetermined section on the recording track, the groove track being continuously formed on the prepit sequence section.
Further in accordance with the present invention, there is also provided an optical read/write apparatus, comprising: a spindle motor rotating an optical recording medium on which a land track and a groove track are formed as a recording track, the optical recording medium including a prepit sequence formed on a middle position between the land track and the neighboring groove track at predetermined intervals on the recording track, the groove track being continuously formed on the prepit sequence section; an optical head irradiating an optical beam on the optical recording medium rotated to read and write information; and an optical detector detecting a signal corresponding to the information from a reflected light on the optical recording medium.